The present invention relates to a shielded cable having a plurality of conductive element wires braided to form an overally-shielding layer around an assembly of one or more insulated core wires, and more particularly to an improvement of braided conductors forming the shielding layer.
In a case where a conventional cable is used in applications where good shielding characteristics at high frequencies are required, it has been so designed that metallic element wires such as those made of tin-plated copper or tin-plated copper alloy are braided around an assembly of one or more insulated core wires to be accommodated in the cable. The shielded cable is also used in applications where not only good shielding characteristics but also high mechanical characteristics including flexibility and resistance to bending and elongation are required. These rigorous requirements cannot be satisfactorily met by the shielding member solely composed of braided metallic element wires because the breaking of these wires is unavoidable during service and the shielding effect is deteriorated .
On the other hand, with a view to providing improved mechanical characteristics, a multicore cable or coaxial having spun stainless steel strands braided to form an overall shield have been used commercially.
Ultrafine coaxial multicore cables for use in the wire harness of a medical instrument, a measuring instrument or the like are required to satisfy not only good mechanical characteristics such as flexibility and resistance to bending and elongation, but also good electrical characteristics such as effective shielding of extraneous electrical noise. Conventional shields composed of braided tin-plated copper or copper alloy wires are poor in mechanical characteristics. On the other hand, conventional shields in which spun stainless steel yarns are braided are so poor in electrical characteristics that they become considerably degraded in shielding effect at frequencies exceeding 1 MHz and at frequencies around 10 MHz, their shielding effect is no better than that of the unshielded multicore or coaxial cable. Particularly, shields solely composed of tin-plated copper or copper alloy wires have a good shielding effect, but they are so poor in mechanical characteristics that when placed under stresses such as bending, various phenomena will occur that render further use of the cable impossible, such as breaking of element wires in the braid, shorting due to contact between broken element wires and core wires in the cable, and breaking of core wires due to abrasion between braided element wires and the core assembly.